idendr0: Interactive Dendrograms

Interactive dendrogram that enables the user to select and
color clusters, to zoom and pan the dendrogram, and to visualize
the clustered data not only in a built-in heat map, but also in
'GGobi' interactive plots and user-supplied plots.
This is a backport of Qt-based 'idendro'
(<https://github.com/tsieger/idendro>) to base R graphics and
Tcl/Tk GUI.